apt-get question: can someone (well, I) downgrade (successfully) by changing the settings in my /apt/preferences file?

After 18 months of not upgrading I am going to rejoin the living with some sort of regular apt-get upgrade cycle. Debian 'testing'.

Now, if all-things-X: xorg, xserver*, x11-common* etc turn out to be a disaster or disfunctional in testing, which has happened in the past, can I downgrade them to stable by using a long /etc/preferences file of

 : : Package: x11-apps Pin: release n=stable Pin-Priority: 10001 Package: x11-common Pin: release n=stable Pin-Priority: 10001 Package: x11-session-utils Pin: release n=stable Pin-Priority: 10001 Package: x11-utils Pin: release n=stable Pin-Priority: 10001 Package: x11-xfs-utils Pin: release n=stable Pin-Priority: 10001 : : 

etc.

apt-get update;

apt-get dist-upgrade;

If not, how should one downgrade part of a distribution, testing --> stable?

Thanks for any help with this.